Bitumen and bitumen-like materials have been modified with a variety of polymers in order to add strength in a variety of environmental conditions encountered in for example road paving and roof membranes. Both polymer-type and blending/mixing process must be selected to accommodate prevailing requirements in the industry.
As examples of such modification, there can be mentioned:
1. Bitumen sheeting. Styrene-butadiene block copolymers and ethylene-propylene rubbers have been added to provide increased strength.
2. Synthetic binders. Formulations including hydrocarbon tackifier resins which are transparent and can be colored having been made less brittle by including polymers.
3. Road surfaces. Bitumen or asphalt has been modified with styrene-butadiene block copolymers, ethylene propylene rubber, ethylene vinyl acetate and methylacrylate copolymers, propylene-butene copolymers to improve wear resistance. Propylene-butene copolymers (Vestoplast made by Huels AG) have been used to improve physical properties at low temperatures.
4. Thermoplastic road marking. Formulations include hydrocarbon tackifiers ethylene vinyl acetate (EVA) and styrene-isoprene-styrene block copolymer (SIS).
Examples of patent specifications include:
FR 1 368 242; U.S. Pat. No. 3395110; U.S. Pat. No. 3459695; U.S. Pat. No. 4263186; U.S. Pat. No. 3 444 117; GB 2 164 344; GB 1247247; GB 1522852; EP 174 795; EP 351736; U.S. Pat. No. 3 669 918; U.S. Pat. No. 3 790 519.
Dow EP 416 815 discloses the modification of asphalt or bitumen using polymers made with monocyclopentadienyl derivatives and a suitable cocatalyst but no particular polymer types are identified for this application.
U.S. Pat. No. 4263 186 relates to bitumen and polymer containing compositions for making sheets which employs high amounts of ethylene based elastomers and varying amounts of a partially crystalline polyolefin. There is no disclosure of the use of a limited amount of a particular ethylene based copolymer having a crystallinity of less than 18%.
EP 351736 discloses waterproof sheets containing major amounts ethylene based copolymers. Example 9 uses a polymer having a density of 0.88.
GB 1522852 discloses an adhesive composition containing bitumen, block copolymer and a small amount of a thermoplastic polymer having a crystallinity below 60% at 25.degree. C. No reference is made to the specific low crystallinity desired for the construction materials of the invention.
GB 1247247 discloses use of "atactic" ethylene based polymers with less than 20 wt % of crystallinity polymer in amounts of from 3 to 20 wt %. However the paving compositions made thereby employ petrolene which is de-asphalted. The petrolene is not a bitumen as defined herein.
Polymers form one phase mixtures with petrolenes. The text does not suggest using these materials with straight reduced asphalt (from which the petrolene is extracted) and it is believed that the polymers specifically disclosed (atactic polypropylene) would act quite distinctly. The prior art aims to increase the softening point and not to provide a distinct phase which aids cohesion of bitumen at low temperatures.
Many polymers suitable for bitumen modification may be difficult to process with the flexibility desired in the construction industry.
It is amongst the objectives of the invention to provide compositions with improved low temperature properties in construction end-uses which can be processed (mixed or blended) starting from a pelletised form.